What Forests Give

PLYWOOD

Just as the use of sawed boards and timbers made it possible to build a house with less wood than when it was built of whole logs, so the use of what is called "plywood" makes it possible to use still less of it than was needed to build a house of boards and joists and shingles. And since this house requires less wood, and also less labor to put it together, it costs less money.

The making of plywood is based on the old practice of making veneer; that is, of gluing thin sheets of wood together and using them as one piece. Veneer was used for furniture. It did not have to stand any heavy strain. It did not have to be cheap. But in order that plywood might be used for houses, it had to be both strong and cheap—far stronger and cheaper than veneer has ever been. Two things were necessary; a glue better than any known, and sheets of thin wood larger than the distance through a tree trunk. Both of these things we have now, and they were found in this way.

Unrolling a Log

During the World War the Government had a sudden need for airplane propellers. These must be of wood that would not split or warp or break when spun at terrific speed. If pieces of a propeller should break off and fly into space there would be one valuable air pilot the less. For this reason the propeller blades must be made of thin layers of wood. The idea was right, but in order to apply it there was needed a glue stronger, more lasting than any known. The Forest Products Laboratory of the Forest Service was asked to find this glue. During their search for it they discovered one, practically waterproof, which is used in plywood. It looks like heavy, brown, half-transparent tissue paper. A sheet of it is laid between two thin layers of wood and made a part of them by the use of heavy pressure and heat, and it has such a grip that the wood itself will be torn apart before the glue will let go. Without this glue, houses of plywood would not be possible.

But neither would they be possible without the new methods of cutting the wide thin sheets of wood, frequently 6 feet wide, from trees with a diameter much less than this. To get these, a log is stripped of its bark and soaked and steamed till it is somewhat softened. Then it is put into a machine something like a turning lathe and set revolving against a long knife which cuts a thin layer from it. Round and round it goes as though it were a bolt of silk being unrolled. Douglas fir is being unrolled in this way and used as the veneer of plywood. Upon the surface of a table or the side of a wall it makes a pattern of great beauty and of a rich golden color. No wallpaper, no plaster, no other covering is necessary.

House of Plywood

Plywood is not used as ordinary boards are used in the building of houses. It is made into units of standard sizes, such as 8 by 4 feet. Each unit is made of two layers of plywood, one glued to each side of an internal framework with an air space between—seasoned so that it will not warp or shrink, glued so that it will not split, made to interlock along the edge with the next unit, and forming both the inside and outside surface of the wall of the house.

Other units have been developed which will make both the ceiling of one room and the floor of the one above. The surfaces of these plywood units can be of any sort of lovely wood veneer, with any sort of beautiful finish. All the other units of house building that can be made of wood have been worked out in standard sizes, and of them has been built by the Forest Products Laboratory in Madison, Wis., a model house of five rooms, which can be set up by seven men in 21 hours and will cost no more than $1,400. This is a charming house, a livable house, a house easy to operate, and easy for the breadwinner to pay for, and built of far fewer trees than the houses of our great-grandfathers. It is part of the answer to the question of how 127,000,000 people can get all the wood they need from 615,000,000 acres of forest land.

But that house has still the final and greatest drawback to the use of wood—it is not fireproof. However, scientists have solved many harder problems than fireproofing wood. In the Forest Products Laboratory is a long room full of intent men turning flame upon wood which has been soaked in chemicals or coated with metallic paint. They raise the heat and lower it to see just how high a temperature it will stand; they blow air upon it in imitation of a high wind; they cool it to find out how long it will hold enough heat to set fire to whatever it touches; and they test it as they tested the strength of glue, over and over again, and write down just what has happened to each stick of wood. They hang these tested woods in long rows, each one carefully labeled with the name of the wood, what was done to make it fireproof, how much heat was applied to it and for how long; and the result—whether it actually caught fire or merely rose in blisters or charred. They have not yet found the perfect way to fireproof wood.

Testing Wood for Fire

There are several forms in which small sections of wood are built into larger units and used as one piece—the old veneer, the newer plywood, and laminated wood are among them. These are used in different ways for different purposes, but the underlying idea is the same in all. In places plywood can even be used as a substitute for steel.

The great beams of wood, each one the trunk of a huge tree, which were all that our ancestors had to hold up their roofs, will splinter and break under heavy weight. Steel beams are not only stronger than a tree trunk; but also they can be made longer than any tree could grow. Steel girders will not crack or break under far heavier loads than a solid beam of wood will bear. We could not have our great skyscrapers nor our long bridges without steel beams. But laminated wood of thin sheets, plywood, or smaller beams overlapping, are much stronger than single beams. Just how strong can they be made? Just how far can they take the place of steel?

The Forest Products Laboratory has a vast, terrifying machine that lays hold of a great arch made of wood which has been centuries growing and begins to put torturing strains upon it. The pressure becomes fiercer, increasing pound by pound to 1,000,000 pounds if the arch can withstand as much pressure as that before it splinters and breaks. But this metal monster is as much a safety device as chains on an automobile tire, or the guard over a buzz saw, for under this testing and retesting it has been found that the arches and beams made up of layers of wood glued together under pressure can be put to some of the uses that solid wood is not strong enough for.

A Million Pounds Pressure Can Be Put Upon the Arch

Arches of Wood Can Take the Place of Steel

A great storehouse of the Forest Products Laboratory is spanned by arches of this laminated wood which have been treated with a protective finish that gives them a luminous glow, as though one could look down through the surface of the wood into the heart of it. Arches like these are lighter and cheaper than steel arches, and up to the span of 100 feet are quite as able as steel to stand the strain put on them.

And there can always be plenty of wood arches. Long after the last pound of iron ore from such great deposits as the Mesaba Range has been sent to the smelter, has been made into pig iron, and the pig iron has become steel girders, and the steel girders have worn away and rusted away, there can be arches of wood—so long as we take the trouble to grow trees!